diff --git a/gfx/public/nsIImage.h b/gfx/public/nsIImage.h
index b7e08398d73..f1f142ade65 100644
--- a/gfx/public/nsIImage.h
+++ b/gfx/public/nsIImage.h
@@ -258,9 +258,22 @@ public:
    */
   NS_IMETHOD UnlockImagePixels(PRBool aMaskPixels) = 0;
 
-#ifdef MOZ_CAIRO_GFX
+  /**
+   * GetSurface
+   * Return the Thebes gfxASurface in aSurface.
+   *
+   * aSurface will be AddRef'd (as with most getters), so
+   * getter_AddRefs should be used.
+   */
   NS_IMETHOD GetSurface(gfxASurface **aSurface) = 0;
-#endif
+
+  /**
+   * SetHasNoAlpha
+   *
+   * Hint to the image that all the pixels are fully opaque, even if
+   * the original format requested a 1-bit or 8-bit alpha mask
+   */
+  virtual void SetHasNoAlpha() = 0;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsIImage, NS_IIMAGE_IID)
diff --git a/gfx/src/shared/gfxImageFrame.cpp b/gfx/src/shared/gfxImageFrame.cpp
index 76eb6810c20..da09fb57a01 100644
--- a/gfx/src/shared/gfxImageFrame.cpp
+++ b/gfx/src/shared/gfxImageFrame.cpp
@@ -551,4 +551,3 @@ NS_IMETHODIMP gfxImageFrame::GetInterface(const nsIID & aIID, void * *result)
 
   return NS_NOINTERFACE;
 }
- 
diff --git a/gfx/src/thebes/nsThebesImage.cpp b/gfx/src/thebes/nsThebesImage.cpp
index 4fbc3a4e3b0..8ec3fec62f1 100644
--- a/gfx/src/thebes/nsThebesImage.cpp
+++ b/gfx/src/thebes/nsThebesImage.cpp
@@ -606,3 +606,16 @@ nsThebesImage::ShouldUseImageSurfaces()
 
     return PR_FALSE;
 }
+
+// A hint from the image decoders that this image has no alpha, even
+// though we created is ARGB32.  This changes our format to RGB24,
+// which in turn will cause us to Optimize() to RGB24.  Has no effect
+// after Optimize() is called, though in all cases it will be just a
+// performance win -- the pixels are still correct and have the A byte
+// set to 0xff.
+void
+nsThebesImage::SetHasNoAlpha()
+{
+    if (mFormat == gfxASurface::ImageFormatARGB32)
+        mFormat = gfxASurface::ImageFormatRGB24;
+}
diff --git a/gfx/src/thebes/nsThebesImage.h b/gfx/src/thebes/nsThebesImage.h
index 5e8915fafe6..0ff8103d3bf 100644
--- a/gfx/src/thebes/nsThebesImage.h
+++ b/gfx/src/thebes/nsThebesImage.h
@@ -103,6 +103,8 @@ public:
         return mImageSurface;
     }
 
+    void SetHasNoAlpha();
+
 protected:
     static PRBool AllowedImageSize(PRInt32 aWidth, PRInt32 aHeight) {
         NS_ASSERTION(aWidth > 0, "invalid image width");
diff --git a/gfx/thebes/public/gfxPlatform.h b/gfx/thebes/public/gfxPlatform.h
index 32881e2abda..82d3bebb366 100644
--- a/gfx/thebes/public/gfxPlatform.h
+++ b/gfx/thebes/public/gfxPlatform.h
@@ -134,12 +134,6 @@ public:
     virtual gfxFontGroup *CreateFontGroup(const nsAString& aFamilies,
                                           const gfxFontStyle *aStyle) = 0;
 
-    /* Returns PR_TRUE if the given block of ARGB32 data really has alpha, otherwise PR_FALSE */
-    static PRBool DoesARGBImageDataHaveAlpha(PRUint8* data,
-                                             PRUint32 width,
-                                             PRUint32 height,
-                                             PRUint32 stride);
-
     void GetPrefFonts(const char *aLangGroup, nsString& array, PRBool aAppendUnicode = PR_TRUE);
 
     /**
diff --git a/gfx/thebes/src/gfxPlatform.cpp b/gfx/thebes/src/gfxPlatform.cpp
index 45c6c72fb90..62ad1b1ab0a 100644
--- a/gfx/thebes/src/gfxPlatform.cpp
+++ b/gfx/thebes/src/gfxPlatform.cpp
@@ -181,26 +181,6 @@ gfxPlatform::SetUseGlitz(PRBool use)
     gGlitzState = (use ? 1 : 0);
 }
 
-PRBool
-gfxPlatform::DoesARGBImageDataHaveAlpha(PRUint8* data,
-                                        PRUint32 width,
-                                        PRUint32 height,
-                                        PRUint32 stride)
-{
-    PRUint32 *r;
-
-    for (PRUint32 j = 0; j < height; j++) {
-        r = (PRUint32*) (data + stride*j);
-        for (PRUint32 i = 0; i < width; i++) {
-            if ((*r++ & 0xff000000) != 0xff000000) {
-                return PR_TRUE;
-            }
-        }
-    }
-
-    return PR_FALSE;    
-}
-
 already_AddRefed<gfxASurface>
 gfxPlatform::OptimizeImage(gfxImageSurface *aSurface)
 {
@@ -208,17 +188,6 @@ gfxPlatform::OptimizeImage(gfxImageSurface *aSurface)
 
     gfxASurface::gfxImageFormat realFormat = aSurface->Format();
 
-    if (realFormat == gfxASurface::ImageFormatARGB32) {
-        // this might not really need alpha; figure that out
-        if (!DoesARGBImageDataHaveAlpha(aSurface->Data(),
-                                        surfaceSize.width,
-                                        surfaceSize.height,
-                                        aSurface->Stride()))
-        {
-            realFormat = gfxASurface::ImageFormatRGB24;
-        }
-    }
-
     nsRefPtr<gfxASurface> optSurface = CreateOffscreenSurface(surfaceSize, realFormat);
 
     if (!optSurface)
diff --git a/gfx/thebes/src/gfxWindowsSurface.cpp b/gfx/thebes/src/gfxWindowsSurface.cpp
index bbc60c3526a..229eb89c821 100644
--- a/gfx/thebes/src/gfxWindowsSurface.cpp
+++ b/gfx/thebes/src/gfxWindowsSurface.cpp
@@ -119,16 +119,6 @@ already_AddRefed<gfxWindowsSurface>
 gfxWindowsSurface::OptimizeToDDB(HDC dc, const gfxIntSize& size, gfxImageFormat format)
 {
     gfxImageFormat realFormat = format;
-    if (realFormat == ImageFormatARGB32) {
-        cairo_surface_t *isurf = cairo_win32_surface_get_image(CairoSurface());
-        if (isurf && !gfxPlatform::DoesARGBImageDataHaveAlpha(cairo_image_surface_get_data(isurf),
-                                                              cairo_image_surface_get_width(isurf),
-                                                              cairo_image_surface_get_height(isurf),
-                                                              cairo_image_surface_get_stride(isurf)))
-        {
-            realFormat = ImageFormatRGB24;
-        }
-    }
 
     if (realFormat != ImageFormatRGB24)
         return nsnull;
diff --git a/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp b/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp
index c7fcc8b55bb..c48530e4f97 100644
--- a/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp
+++ b/modules/libpr0n/decoders/gif/nsGIFDecoder2.cpp
@@ -77,6 +77,9 @@ mailing address.
 #include "prlog.h"
 #include "GIF2.h"
 
+#include "nsIImage.h"
+#include "nsIInterfaceRequestorUtils.h"
+
 #include "nsGIFDecoder2.h"
 #include "nsIInputStream.h"
 #include "nsIComponentManager.h"
@@ -320,6 +323,7 @@ void nsGIFDecoder2::EndGIF()
 void nsGIFDecoder2::BeginImageFrame()
 {
   mImageFrame = nsnull; // clear out our current frame reference
+  mFrameHasNoAlpha = PR_TRUE;
 
   if (!mGIFStruct.images_decoded) {
     // Send a onetime OnDataAvailable (Display Refresh) for the first frame
@@ -350,6 +354,11 @@ void nsGIFDecoder2::EndImageFrame()
     // timeout for the image until here to help ensure that we have the whole 
     // image frame decoded before we go off and try to display another frame.
     mImageFrame->SetTimeout(mGIFStruct.delay_time);
+
+    if (mFrameHasNoAlpha) {
+      nsCOMPtr<nsIImage> img(do_GetInterface(mImageFrame));
+      img->SetHasNoAlpha();
+    }
   }
   mImageContainer->EndFrameDecode(mGIFStruct.images_decoded, mGIFStruct.delay_time);
 
@@ -442,12 +451,14 @@ void nsGIFDecoder2::HaveDecodedRow(
     } else {
       PRUint8* rowBufIndex = aRowBufPtr;
       PRUint32* rgbRowIndex = (PRUint32*)mRGBLine;
+      PRBool rowHasNoAlpha = PR_TRUE;
 
       const PRInt32 tpixel = 
         mGIFStruct.is_transparent ? mGIFStruct.tpixel : -1;
 
       while (rowBufIndex != mGIFStruct.rowend) {
         if (*rowBufIndex >= cmapsize || *rowBufIndex == tpixel) {
+          rowHasNoAlpha = PR_FALSE;
           *rgbRowIndex++ = 0x00000000;
           ++rowBufIndex;
           continue;
@@ -462,6 +473,8 @@ void nsGIFDecoder2::HaveDecodedRow(
       }
       for (int i=0; i<aDuplicateCount; i++)
         mImageFrame->SetImageData(mRGBLine, bpr, (aRowNumber+i)*bpr);
+      if (!rowHasNoAlpha)
+        mFrameHasNoAlpha = PR_FALSE;
     }
 
     mCurrentRow = aRowNumber + aDuplicateCount - 1;
diff --git a/modules/libpr0n/decoders/gif/nsGIFDecoder2.h b/modules/libpr0n/decoders/gif/nsGIFDecoder2.h
index 020c5e974d5..98e1124f271 100644
--- a/modules/libpr0n/decoders/gif/nsGIFDecoder2.h
+++ b/modules/libpr0n/decoders/gif/nsGIFDecoder2.h
@@ -102,6 +102,7 @@ private:
   PRUint8 mCurrentPass;
   PRUint8 mLastFlushedPass;
   PRPackedBool mGIFOpen;
+  PRPackedBool mFrameHasNoAlpha;
 
   gif_struct mGIFStruct;
 };
diff --git a/modules/libpr0n/decoders/png/nsPNGDecoder.cpp b/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
index 85f0216e981..59b81421621 100644
--- a/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
+++ b/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
@@ -119,6 +119,8 @@ void nsPNGDecoder::CreateFrame(png_uint_32 x_offset, png_uint_32 y_offset,
   
   if (mObserver)
     mObserver->OnStartFrame(nsnull, mFrame);
+
+  mFrameHasNoAlpha = PR_TRUE;
 }
 
 // set timeout and frame disposal method for the current frame
@@ -648,6 +650,7 @@ row_callback(png_structp png_ptr, png_bytep new_row,
     PRUint32 imageDataLength, bpr = width * sizeof(PRUint32);
     decoder->mFrame->GetImageData(&imageData, &imageDataLength);
     PRUint32 *cptr32 = (PRUint32*)(imageData + (row_num*bpr));
+    PRBool rowHasNoAlpha = PR_TRUE;
 
     if (decoder->mTransform) {
       if (decoder->mCMSLine) {
@@ -679,6 +682,8 @@ row_callback(png_structp png_ptr, png_bytep new_row,
       {
         for (PRUint32 x=iwidth; x>0; --x) {
           *cptr32++ = GFX_PACKED_PIXEL(line[3]?0xFF:0x00, line[0], line[1], line[2]);
+          if (line[3] == 0)
+            rowHasNoAlpha = PR_FALSE;
           line += 4;
         }
       }
@@ -688,12 +693,17 @@ row_callback(png_structp png_ptr, png_bytep new_row,
       {
         for (PRUint32 x=width; x>0; --x) {
           *cptr32++ = GFX_PACKED_PIXEL(line[3], line[0], line[1], line[2]);
+          if (line[3] != 0xff)
+            rowHasNoAlpha = PR_FALSE;
           line += 4;
         }
       }
       break;
     }
 
+    if (!rowHasNoAlpha)
+      decoder->mFrameHasNoAlpha = PR_FALSE;
+
     nsIntRect r(0, row_num, width, 1);
     nsCOMPtr<nsIImage> img(do_GetInterface(decoder->mFrame));
     img->ImageUpdated(nsnull, nsImageUpdateFlags_kBitsChanged, &r);
@@ -714,6 +724,10 @@ frame_info_callback(png_structp png_ptr, png_uint_32 frame_num)
   if (!(decoder->apngFlags & FRAME_HIDDEN)) {
     PRInt32 timeout;
     decoder->mFrame->GetTimeout(&timeout);
+    if (decoder->mFrameHasNoAlpha) {
+      nsCOMPtr<nsIImage> img(do_GetInterface(decoder->mFrame));
+      img->SetHasNoAlpha();
+    }
     decoder->mImage->EndFrameDecode(frame_num, timeout);
     decoder->mObserver->OnStopFrame(nsnull, decoder->mFrame);
   }
@@ -753,6 +767,10 @@ end_callback(png_structp png_ptr, png_infop info_ptr)
   if (!(decoder->apngFlags & FRAME_HIDDEN)) {
     PRInt32 timeout;
     decoder->mFrame->GetTimeout(&timeout);
+    if (decoder->mFrameHasNoAlpha) {
+      nsCOMPtr<nsIImage> img(do_GetInterface(decoder->mFrame));
+      img->SetHasNoAlpha();
+    }
     decoder->mImage->EndFrameDecode(decoder->mPNG->num_frames_read, timeout);
   }
   
diff --git a/modules/libpr0n/decoders/png/nsPNGDecoder.h b/modules/libpr0n/decoders/png/nsPNGDecoder.h
index 9fc3f15da2a..a0b00c5f9f5 100644
--- a/modules/libpr0n/decoders/png/nsPNGDecoder.h
+++ b/modules/libpr0n/decoders/png/nsPNGDecoder.h
@@ -93,6 +93,7 @@ public:
   PRUint8 apngFlags;
   PRUint8 mChannels;
   PRPackedBool mError;
+  PRPackedBool mFrameHasNoAlpha;
 };
 
 #endif // nsPNGDecoder_h__
diff --git a/modules/libpr0n/decoders/xbm/Makefile.in b/modules/libpr0n/decoders/xbm/Makefile.in
index 51f04bf739b..3334742a5aa 100644
--- a/modules/libpr0n/decoders/xbm/Makefile.in
+++ b/modules/libpr0n/decoders/xbm/Makefile.in
@@ -52,6 +52,7 @@ LIBXUL_LIBRARY  = 1
 REQUIRES	= xpcom \
 		  gfx \
 		  imglib2 \
+		  thebes \
 		  $(NULL)
 
 CPPSRCS        = nsXBMDecoder.cpp
diff --git a/modules/libpr0n/decoders/xbm/nsXBMDecoder.cpp b/modules/libpr0n/decoders/xbm/nsXBMDecoder.cpp
index 835698338a7..d2bf215f40c 100644
--- a/modules/libpr0n/decoders/xbm/nsXBMDecoder.cpp
+++ b/modules/libpr0n/decoders/xbm/nsXBMDecoder.cpp
@@ -47,19 +47,14 @@
 
 #include "nsIInputStream.h"
 #include "nsIComponentManager.h"
+#include "nsIImage.h"
+#include "nsIInterfaceRequestorUtils.h"
 
 #include "imgILoad.h"
 
 #include "nsIProperties.h"
 #include "nsISupportsPrimitives.h"
 
-#if defined(XP_WIN) || defined(XP_OS2) || defined(XP_BEOS) || defined(MOZ_WIDGET_PHOTON)
-#define GFXFORMAT gfxIFormats::BGR_A1
-#else
-#define USE_RGB
-#define GFXFORMAT gfxIFormats::RGB_A1
-#endif
-
 NS_IMPL_ISUPPORTS1(nsXBMDecoder, imgIDecoder)
 
 nsXBMDecoder::nsXBMDecoder() : mBuf(nsnull), mPos(nsnull), mAlphaRow(nsnull)
@@ -92,12 +87,18 @@ NS_IMETHODIMP nsXBMDecoder::Init(imgILoad *aLoad)
 
     mCurRow = mBufSize = mWidth = mHeight = 0;
     mState = RECV_HEADER;
+    mHasNoAlpha = PR_TRUE;
 
     return NS_OK;
 }
 
 NS_IMETHODIMP nsXBMDecoder::Close()
 {
+    if (mHasNoAlpha) {
+        nsCOMPtr<nsIImage> img(do_GetInterface(mFrame));
+        img->SetHasNoAlpha();
+    }
+
     mObserver->OnStopContainer(nsnull, mImage);
     mObserver->OnStopDecode(nsnull, NS_OK, nsnull);
     mObserver = nsnull;
@@ -185,7 +186,7 @@ nsresult nsXBMDecoder::ProcessData(const char* aData, PRUint32 aCount) {
         mImage->Init(mWidth, mHeight, mObserver);
         mObserver->OnStartContainer(nsnull, mImage);
 
-        nsresult rv = mFrame->Init(0, 0, mWidth, mHeight, GFXFORMAT, 24);
+        nsresult rv = mFrame->Init(0, 0, mWidth, mHeight, gfxIFormats::RGB_A1, 24);
         if (NS_FAILED(rv))
             return rv;
 
@@ -240,6 +241,7 @@ nsresult nsXBMDecoder::ProcessData(const char* aData, PRUint32 aCount) {
         PRUint32 abpr;
         mFrame->GetAlphaBytesPerRow(&abpr);
         PRBool hiByte = PR_TRUE;
+        PRBool chunkHasNoAlpha = PR_TRUE;
 
         do {
             PRUint32 pixel = strtoul(mPos, &endPtr, 0);
@@ -273,6 +275,8 @@ nsresult nsXBMDecoder::ProcessData(const char* aData, PRUint32 aCount) {
             for (int i = 0; i < alphas; i++) {
                 const PRUint8 val = ((pixel & (1 << i)) >> i) ? 255 : 0;
                 *ar++ = (val << 24) | 0;
+                if (val == 0)
+                    chunkHasNoAlpha = PR_FALSE;
             }
 
             mCurCol = PR_MIN(mCurCol + 8, mWidth);
@@ -297,6 +301,9 @@ nsresult nsXBMDecoder::ProcessData(const char* aData, PRUint32 aCount) {
             if (*mPos == ',')
                 mPos++;
         } while ((mState == RECV_DATA) && *mPos);
+
+        if (!chunkHasNoAlpha)
+            mHasNoAlpha = PR_FALSE;
     }
 
     return NS_OK;
diff --git a/modules/libpr0n/decoders/xbm/nsXBMDecoder.h b/modules/libpr0n/decoders/xbm/nsXBMDecoder.h
index 77cf1ffee2c..34cde061336 100644
--- a/modules/libpr0n/decoders/xbm/nsXBMDecoder.h
+++ b/modules/libpr0n/decoders/xbm/nsXBMDecoder.h
@@ -90,6 +90,7 @@ private:
 
     PRPackedBool mIsCursor;
     PRPackedBool mIsX10; // X10 flavor XBM?
+    PRPackedBool mHasNoAlpha;
 
     enum {
         RECV_HEADER,